In the following description, a procedure for requesting a random access uplink resource in a broadband wireless access system is explained.
FIG. 1 shows a 3-step uplink resource request procedure executable in a general IEEE 802.16 system.
Referring to FIG. 1, a mobile station (AMS) sends a quick access message including a bandwidth request (BR) preamble sequence (i.e., BR code), an uplink bandwidth request information (e.g., station ID, BR index indicating a size of a requested resource, etc.) and the like to a base station (S101).
The base station may transmit a reception state of the BR preamble sequence and the quick access message, which were sent by each mobile station, to the corresponding mobile station via a bandwidth request acknowledgement A-MAP information element (BR ACK A-MAP IE) [S102].
If the base station normally receives the BR preamble sequence and the quick access message sent by the mobile station, it may allocate an uplink (UL) resource to the corresponding mobile station via an uplink basic assignment A-MAP information element (UL basic assignment A-MAP IE) [S103].
The mobile station may be able to transmit data to the base station via the allocated UL resource [S104].
FIG. 2 shows a 5-step uplink resource request procedure executable in a general IEEE 802.16 system.
FIG. 2 assumes a fall-back mode corresponding to a case that a quick access message is lost. Referring to FIG. 2, a mobile station (AMS) sends a quick access message including a bandwidth request (BR) preamble sequence (i.e., BR code), an uplink bandwidth request information (e.g., station ID, BR index indicating a size of a requested resource, etc.) and the like to a base station (S201).
In this case, the base station is not able to normally decode the quick access message due to transmission error [S202].
The base station may transmit a reception state of the BR preamble sequence and the quick access message, which were sent by each mobile station, to the corresponding mobile station via a bandwidth request acknowledgement A-MAP information element (BR ACK A-MAP IE) [S203].
If the base station normally receives the BR preamble sequence transmitted by the mobile station only, since the base station may be unable to know a size of a resource requested by the mobile station, the mobile station allocates a UL resource for transmitting a bandwidth to the mobile station via CDMA allocation A-MAP IE [S204].
The mobile station sends a BW-REQ message (e.g., a header type) including information of the resource requested by the mobile station to the base station via the allocated resource [S205].
If the base station receives the BE-REQ message sent by the mobile station, it may allocate an uplink (UL) resource to the corresponding mobile station via an uplink basic assignment A-MAP information element (UL basic assignment A-MAP IE) [S206].
The mobile station may be able to transmit data to the base station via the allocated UL resource [S207].
In case that the mobile station does not send the quick access message to the base station, it may become a general 5-step bandwidth request procedure.
FIG. 3 shows one example of an initial/handover ranging procedure executable in a general IEEE 802.16 system.
Referring to FIG. 3, first of all, a mobile station transmits a ranging preamble code for the usage of initial/handover ranging to a base station [S301].
The base station may send a ranging acknowledgement (AAI_RNG-ACK) message including a received state and a physical (PHY) adjustment value (e.g., timing, power, frequency, etc.) for a ranging preamble code transmitted by each mobile station to the corresponding mobile station [S302].
Having normally received the ranging preamble code, the base station allocates a UL resource required for the mobile station to send a ranging request (AAI_RNG-REQ) message to the mobile station via CDMA allocation A-MAP IE [S303].
The mobile station sends AAI_RNG-REQ message to the base station via the allocated UL resource [S304].
In response to the AAI_RNG-REQ message sent by the mobile station, the base station sends a ranging response (AAI_RNG-RSP) to the mobile station [S305].
FIG. 4 shows one example of a periodic ranging procedure executable in a general IEEE 802.16 system.
Referring to FIG. 4, a mobile station transmits a ranging preamble code for the usage of periodic ranging to a base station [S401].
The base station may send a ranging acknowledgement (AAI_RNG-ACK) message including a received state and a physical (PHY) adjustment value (e.g., timing, power, frequency, etc.) for a ranging preamble code transmitted by each mobile station to the corresponding mobile station [S402].
In order for a mobile station to transmit a preamble code to a base station in the random access procedures described with reference to FIGS. 1 to 4, a region (i.e., RA region) for the mobile station to perform a random access should exist in a frame or a subframe corresponding to a unit smaller than that of the frame. This random access region (RA region) may be divided into a bandwidth request region (BR region) for the mobile station to request a UL resource allocation and a ranging region for the mobile station to attempt a ranging. One example of arranging this random access region is described with reference to FIG. 5 as follows.
FIG. 5 shows one example of an arrangement type of a random access region if a downlink-to-uplink ratio is 5:3 in a general IEEE 802.16 system.
Referring to FIG. 5, there is a random access region arranged in a 3rd frame of a 1st superframe. In particular, as mentioned in the foregoing description, the random access region may include bandwidth request regions 510 and 530 and a ranging region 520.
A base station may transmit a BR preamble sequence list and the like successfully received via the bandwidth request (BR) region to a mobile station via BR ACK A-MAP and may transmit a ranging preamble code list and the like successfully received via the ranging region to the mobile station via AAI_RNG-ACK message.
Based on the ACK information, the mobile terminal may be able to recognize whether its random access attempt has been successful. Therefore, the mobile station should check whether the above-mentioned ACK information is transmitted each subframe. If the ACK information is transmitted as a broadcast, the mobile station should decode the corresponding message or A-MAP to check a message of a different type or a type of A-MAP.
Therefore, in order for the mobile station not to perform unnecessary decoding, the mobile station should be aware in advance whether the corresponding data contains the ACK information (i.e., BR ACK A-MAP or AAI_RNG-ACK) until decoding the contents of the corresponding data.